This invention relates to a method of controlling the operating amount of an operation control means for an internal combustion engine, and more particularly to a method of this kind which is adapted to correct the operating amount of such operation control means in a manner responsive to atmospheric pressure for improvement of the driveability of the engine over all operating regions of the engine inclusive of low load operating regions such as an idling region.
A method has been proposed, e.g. by Japanese Provisional Patent Publications (Kokai) Nos. 58-85337, 54-153929, and 58-88429, which determines a basic operating amount of operation control means for controlling the operation of the engine, such as a basic fuel injection amount to be supplied to the engine by a fuel supply quantity control system, a basic value of spark ignition timing to be controlled by an ignition timing control system, and a basic recirculation amount of exhaust gases to be controlled by an exhaust gas recirculation control system, in dependence on values of engine operating parameters indicative of the intake air quantity supplied to the engine, such as absolute pressure in the intake pipe of the engine downstream of a throttle valve therein and engine rotational speed, and corrects the basic operating amount thus determined in response to atmospheric pressure, to thereby set a desired operating amount for the operation control means with accuracy. The ground for correcting the operating amount in response to atmospheric pressure lies in that the back pressure or pressure of exhaust gases varies with a change in the atmospheric pressure to vary the quantity of air sucked into the engine cylinders per suction stroke even if absolute pressure in the intake pipe remains constant. However, while the engine is operating in a low load condition such as at idle, the intake pipe absolute pressure has a reduced rate of change relative to the lapse of time with respect to a rate of change in the engine rotational speed relative to the lapse of time. Therefore, according to the above proposed method of determining operating amounts of the operation control means in dependence on the intake pipe absolute pressure and the engine rotational speed (generally called "the speed density method", and hereinafter merely referred to as "the SD method"), it is difficult to set with accuracy an operating amount such as a fuel supply quantity in accordance with the state of condition of the engine, thus causing hunting of the engine rotation, during operation of the engine in such a low load condition. In view of the foregoing, a method (hereinafter merely called "the KMe method") has been proposed, e.g. by Japanese Patent Publication No. 52-6414, which is based upon the recognition that the quantity of intake air passing the throttle valve is not dependent upon either of pressure PBA in the intake pipe downstream of the throttle valve and pressure of the exhaust gases while the engine is operating in a particular low load condition wherein the ratio PBA/PA' of intake pipe pressure PBA downstream of the throttle valve to intake pipe pressure PA' upstream of the throttle valve is below a critical pressure ratio (=0.528) at which the intake air forms a sonic flow, and accordingly the quantity of intake air can be determined solely in dependence on the valve opening of the throttle valve, if the intake pipe pressure PA' upstream of the throttle valve remains constant. Therefore, this proposed method detects the valve opening of the throttle valve alone to thereby detect the quantity of intake air with accuracy while the engine is operating in the above-mentioned particular low load condition, and then sets an operating amount such as a fuel injection quantity on the basis of the detected value of the intake air quantity.
However, when the intake pipe pressure PA' upstream of the throttle valve assumes a value other than the standard atmospheric pressure, the KMe method is not appropriate to determine the operating amount with accuracy, requiring correction of the operating amount determined by the use of the KMe method, in response to the actual value of the pressure PA'.